Measuring operations are essential in any machining or other manufacturing process; and, with the growing demand for high precision parts and the concomitant increase in high precision manufacturing techniques, the need for precise measurement is ever increasing. In many machining, manufacturing or maintenance procedures it is necessary to measure the interior diameter of a pipe, tube or bore hole. Such measurements are made for purposes of quality control in the manufacture of new items as well as for purposes of inspecting items in service to detect wear, eccentricity, and to ascertain size.
As used herein, the term "bore hole gaging" shall refer to any measurement of the interior diameter of a workpiece, be it an internal diameter formed by boring, or other machining process as well as an internal diameter formed by casting, extruding, or other such techniques.
The simplest of bore hole measuring techniques involve mechanical operations utilizing tools such as calipers. In more sophisticated variations of this technique, mechanical measuring devices may be equipped with indicating means such as an electronic transducer to provide a quicker and more accurate reading. One such apparatus is shown in U.S. Pat. No. 4,473,956. Problems occur with strictly mechanical measuring devices because of the inherent unreliability and inaccuracy of devices comprised of many moving parts and various mechanical linkages. Additionally, mechanical indicating devices are generally complicated and slow to use.
It will therefore be appreciated that there is a need for accurate, high speed, reliable bore hole gaging devices, particularly devices adapted to interface with electronic data processing systems. A present there are available a number of electronic sensors or transducers capable of providing fast and accurate readings in an output format readily compatible with electronic signal processing. It has previously been proposed to incorporate such sensor technology into bore hole gaging apparatus as will be noted in U.S. Pat. Nos. 4,030,206; 4,420,889; and 4,386,462. While the aforedescribed apparatus do provide for electronic bore hole gaging, none of the foregoing includes means for accurately centering the gage in the bore hole being measured. While accurate readings may be provided by electronic sensors, if such sensors are not precisely positioned along the diameter of the bore hole, an inaccurate reading will result. Furthermore, all of the aforementioned apparatus include 2 "live" measuring centers, that is two sensors directly coupled to a transducer. It is believed that greater accuracy would ensue if only a single live center were employed in conjunction with a relatively immobile or fixed reference measuring point.
The present invention provides for an improved bore hole gaging apparatus which is designed to be self-centering. The apparatus of the present invention is ideally suited for automated measuring of bore hole size because of the inclusion of this self-centering feature. Additionally, the gage of the present invention includes a single live measuring point, thereby increasing its accuracy and reliability. These and other advantages of the present invention will be readily apparent from the drawings, discussion and description which follow.